I wonder why...
 

...the car DID start at all? See attached pictures.

It has been torrential rain here for 3 days and the car had been parked outside. Yesterday the car (964 MY90) would not start.
First I suspected the DME relay but after some research I am pretty sure the alarm unit had something to do with it (see pictures).

But now to the question:

Do I need to bridge more than "15" and "87c" which re-connects the DME relay? Which made the car start nicely.

If I read the alarm unit schematics correctly (attached pict) this is the layout:
30 is power supply (+12V)
Hn Horn
61 This I cannot understand!
31 Flashing of the lights
A Signal from Lock "Open"
87a To DME Relay
MK Doors or hoods switches
T- Door Switch?
E Signal from Lock "Locked"
15 input voltage destined for the DME relay
Attachment 336776

Attachment 336777